In the weeks that followed, the control measures were expanded to include banning the transfer of farm animals, quarantining farms where the disease had been found, closing certain regions to tourists, and requiring safety precautions such as the use of disinfectant on clothing, boots, and vehicles in rural areas.
As the epidemic peaked in early April, the government imposed the culling policy requiring that all infected animals be slaughtered immediately.
"There was quite a lot of opposition to culling from different groups in the farming community, and to a lesser degree from the general public, mostly asking why we didn't use vaccination and questioning whether the culling was really necessary," said Neil M. Ferguson, lead author of the study reported in Nature.
In addition to the immediate slaughter of infected animals, several other culling strategies were used during the outbreak, and the merits of the policy have been the subject of heated debate.
The culling was required not only on farms whose animals were infected but also on adjacent farms and on farms where the infection may have been transferred through the movement of animals, people, or vehicles or through airborne transmission.
In the hardest hit regions, such as Cumbria, Dumfries, and Galloway, even more extensive slaughter policies were imposed.
"Our results indicate that if only infected premises were culled, the epidemic would have been much larger, infecting around 20,000 properties," the authors of the Nature paper concluded. As it was, animals on fewer than 8,000 farms were slaughtered.
The researchers said that if the culling had been done earlier and more intensively on farms adjacent to those whose animals were infected, they believe the move would have dramatically reduced both the number of cases of foot-and-mouth disease and the number of farms affected by the mandated slaughter.
The authors of the Science paper concurred, saying that a speedy response in implementing disease-control strategies—including the culling of animals on neighboring farms—is paramount. They also believe that culling both cattle and sheep, rather than sheep only, could have short-circuited the spread of the epidemic sooner.
Lessons for the Future
This year's foot-and-mouth epidemic in Great Britain affected mainly cows and sheep. Both groups of researchers found that large farms with many animals were more susceptible to outbreaks of the infection, as were farms that had a mix of livestock.
Cattle transmit the disease more readily than sheep, making them more susceptible to the disease. This greater susceptibility may be the result of increased contact with people, vehicles, and other species of livestock rather than an innate biological susceptibility, the researchers noted.
Yet many more sheep were affected because there are far more sheep than cows in Great Britain.
Fragmented farms—those where the fields are scattered—were also found to be at higher risk of transmission, probably because of greater movement of people and vehicles between the patches of land.
The researchers from the University of Cambridge said the use of vaccination as an alternative to or even in conjunction with the culling of animals on neighboring properties as a control strategy is problematic.
First, the incubation period from the time of exposure to infection is about five days. In addition, the period from the onset of infection to when the disease is reported is generally about nine days. At that point, the study noted, vaccinating the livestock on neighboring farms would likely be too little and too late a response.
Both groups also warned that the epidemic is not yet over and any relaxation of movement and biosecurity measures in the months ahead could lead to another outbreak.
"As the weather gets cooler and the virus is able to survive longer, we are in danger of seeing significant outbreaks of the epidemic again," said Christi Donnelly, a member of the Imperial College team.
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